1. Field of the Invention.
This disclosure is related to the field of systems for the management of traffic flow through the controlling of signal lights and monitoring the location of vehicles within a traffic grid.
2. Description of Related Art.
In the perfect commuter utopia, signal lights would automatically switch to green every time a driver's vehicle approached an intersection, creating an unobstructed pathway towards the driver's final destination. In real life though, hitting a red light is a normal and inevitable part of any driver's commute. With the growth of modern cities and the reliance of much of the population on mass transit and personal automobiles for transportation, efficient control of the ebb and flow of traffic through efficient and smart signal light control and coordination systems has become increasingly important.
There are many substantial benefits to be reaped from improved traffic flow for personal, mass transit, and emergency motor vehicles. For many commuters, reclaiming part of their day would enhance their quality of life. Further, less congestion on the roads would generate fewer accidents, thereby saving lives. Moreover, traffic delays impinge on productivity and economic efficiency—time spent traveling to and from work is not time spent doing work. Further, many goods must be transported and many service providers must travel to their clients. Traffic delays all of these economic production factors. There is also a concern regarding the increased pollution that results from stop-and-go traffic flow in contrast to smooth flowing traffic. Further, longer commutes means longer running times and entails more greenhouse gases. Also, congested traffic and uncoordinated signal lights can cause delays in the mass transit system which, if not remedied, can throw off an entire mass transit schedule grid and disincentivise individuals from using mass transit systems. For example, it has been demonstrated that schedule adherence for mass transit vehicles results in an increase in ridership. Lastly, the importance of prioritizing and efficiently moving emergency vehicles through traffic lights is axiomatic.
Currently, a variety of different control and coordination systems are utilized to ensure the smooth and safe management of traffic flows. One commonly utilized mechanism is the traffic controller system. In this system, the timing of a particular signal light is controlled by a traffic controller located inside a cabinet which is at a close proximity to the signal light. Generally, the traffic controller cabinet contains a power panel (to distribute electrical power in the cabinet); a detector interface panel (to connect to loop detectors and other detectors); detector amplifiers; a controller; a conflict motor unit; flash transfer relays; and a police panel (to allow the police to disable and control the signal), amongst other components.
Traffic controller cabinets generally operate on the concept of phases or directions of movement grouped together. For example, a simple four-way intersection will have two phases: North/South and East/West; a four-way intersection with independent control for each direction and each left hand turn will have eight phases. Controllers also generally operate on the concept of rings or different arrays of independent timing sequences. For example, in a dual ring controller, opposing left-turn arrows may turn red independently, depending on the amount of traffic. Thus, a typical controller is an eight-phase, dual ring controller.
The currently utilized control and coordination systems for the typical signal light range from simple clocked timing mechanisms to sophisticated computerized control and coordination systems that self-adjust to minimize the delay to individuals utilizing the roadways.
The simplest control system currently utilized is a timer system. In this system, each phase lasts for a specific duration until the next phase change occurs. Generally, this specific timed pattern will repeat itself regardless of the current traffic flows or the location of a priority vehicle within the traffic grid. While this type of control mechanism can be effective in one-way grids where it is often possible to coordinate signal lights to the posted speed limit, this control mechanism is not advantageous when the signal timing of the intersection would benefit from being adapted to the changing flows of traffic throughout the day.
Dynamic signals, also known as actuated signals, are programmed to adjust their timing and phasing to meet the changing ebb and flow in traffic patterns throughout the day. Generally, dynamic traffic control systems use input from detectors to adjust signal timing and phasing. Detectors are devices that use sensors to inform the controller processor whether vehicles or other road users are present. The signal control mechanism at a given light can utilize the input it receives from the detectors to adequately adjust the length and timing of the phases in accordance with the current traffic volumes and flows. The currently utilized detectors can generally be placed into three main classes: in-pavement detectors, non-intrusive detectors, and detectors for non-motorized road users.
In-pavement detectors are detectors that are located in or underneath the roadway. These detectors typically function similarly to metal detectors or weight detectors, utilizing the metal content or the weight of a vehicle as a trigger to detect the presence of traffic waiting at the light and, thus, can reduce the time period that a green signal is given to an empty road and increase the time period that a green signal is given to a busy throughway during rush hour. Non-intrusive detectors include video image processors, sensors that use electromagnetic waves or acoustic sensors that detect the presence of vehicles at the intersection waiting for the right of way from a location generally over the roadway. Some models of these non-intrusive detectors have the benefit of being able to sense the presence of vehicles or traffic in a general area or virtual detection zone preceding the intersection. Vehicle detection in these zones can have an impact on the timing of the phases. Finally, non-motorized user detectors include demand buttons and specifically tuned detectors for detecting pedestrians, bicyclists and equestrians.
Above and beyond detectors for individual signal lights, coordinated systems that string together and control the timing of multiple signal lights are advantageous in the control of traffic flow. Generally, coordinated systems are controlled from a master controller and are set up so that lights cascade in sequence, thereby allowing a group or “platoon” of vehicles to proceed through a continuous series of green lights. Accordingly, these coordinated systems make it possible for drivers to travel long distances without encountering a red light. Generally, on one-way streets this coordination can be accomplished with fairly constant levels of traffic. Two-way streets are more complicated, but often end up being arranged to correspond with rush hours to allow longer green light times for the heavier volume direction. The most technologically advanced coordinated systems control a series of city-wide signal lights through a centrally controlled system that allows for the signal lights to be coordinated in real-time through above-ground sensors that can sense the levels of traffic approaching and leaving a virtual detection zone which precedes a particular intersection.
While cascading or synchronized central control systems are an improvement on the traditional timer controlled systems, they still have their drawbacks. Namely, priority vehicles in these systems are only able to interact with a virtual detection zone immediately preceding a particular intersection; there is no real-time monitoring of the traffic flows preceding or following this virtual detection zone across a grid of multiple signal lights. Stated differently, there is no real-time monitoring of how a vehicle or a group of vehicles travels through a traffic grid as a whole (i.e., approaching, traveling through and leaving intersections along with a vehicle's transit between intersections). Accordingly, these systems can provide for a priority vehicle, such as an emergency vehicle, to be accelerated through a particular signal at the expense of other vehicles, but they lack the capability to adapt and adjust traffic flows to keep a mass transit vehicle, or similar time scheduled vehicle, on time or adjust the lights in front of a mass transit vehicle to get it back on schedule. Virtual detection zone based systems only have the capability for control of a particular signal light to accelerate the movement of a single vehicle or a group of vehicles approaching that signal directly; they cannot offer an integrated control system with the capability of controlling the phases of multiple signal lights in a grid system, altering the length of particular phases at particular signal lights within the grid system to accommodate a particular vehicle traveling through the grid system according to a relatively fixed path and schedule.
Another problem with virtual detection zone based systems is their disruption of the overall traffic flow of the grid. As noted previously, detection zone based systems are focused on individual signal lights. If a priority vehicle is sensed in the virtual detection zone, the immediately upcoming light will either change to green to give the priority vehicle the right-of-way and potentially disrupt the entire system (something logical for allowing rapid passage of an emergency vehicle) or will not because the vehicle lacks sufficient priority to disrupt the system (as can be the case with a mass transit vehicle) simply to beat the next signal.
What detection zone based systems fail to take into account is the impact this immediate change in an immediately approached signal light phase, irrespective of other traffic at the light, has on the overall traffic flows of the grid as a whole. Thus, while aiding in getting a particular priority vehicle through an intersection, these systems can, on a broader basis, add to rather than decrease the traffic levels in a given area at a given time. Further, because of their focus on a single signal light and vehicles approaching a single signal light, these systems are generally incapable of adjusting a series of lights within the traffic grid based upon a vehicle's current position, speed, schedule and path of travel.
Another frequent traffic problem which cannot be addressed by these commonly utilized virtual detection zone based systems is mass transit vehicle bunching, also known as bus bunching, clumping or platooning. Bunching refers to a group of two or more transit vehicles along the same route, which are scheduled to be evenly spaced, such as buses, catching up with each other and, thus, running in the same location at the same time. Generally, bunching occurs when at least one of the vehicles is unable to keep to its schedule and therefore ends up in the same location as one or more other vehicles on the same route. Thus, the lead mass transit vehicle in the bunch typically slows to pick up passengers that would otherwise be boarding the trailing mass transit vehicle. This leads to overcrowding and further slowing of the lead vehicle. Conversely, the trailing mass transit vehicle encounters fewer passengers and, soon, both mass transit vehicles are in full view of each other—to the dismay of passengers on the overcrowded and behind schedule vehicles. It is no surprise that bunching is a leading complaint of regular transit riders and a headache for those operating and managing transit services. The currently utilized detection zone based systems—with their control methodology localized to individual lights—are simply incapable of controlling or preventing bunching.
Another failing of the currently utilized detection zone based systems is their inability to modify the conditions under which a vehicle may request priority. For example, under many of these currently utilized systems, priority is given to any flagged vehicle that enters a detection zone and is sensed by a detector (such as an in-pavement detector). These systems are generally incapable of granting priority on a more nuanced and conditional basis such as only granting priority when another mass transit vehicle has not requested priority within a specified time frame or only granting priority when an exit request has not been made for the next stop.
Thus, there is a need in the art of traffic flow management for a system that is capable of controlling and adjusting signal lights based on the movement, position and proposed schedules of one or more tracked vehicles within a traffic grid.